RUSBF185-2 Polymeric PTC Resettable Fuse Equivalent & Substitute Parts

Part Overview

The RUSBF185-2 is a Littelfuse PolySwitch® polymeric PTC resettable fuse designed for overcurrent protection in electronic circuits. This through-hole radial disc component operates at 16V with a 1.85A hold current and provides automatic reset functionality after fault conditions are cleared. The part is actively manufactured and widely stocked, with 4040 units available in inventory. Alternative part numbers exist within the same product family to support supply chain flexibility and regional availability requirements.

Key Parameters

Parameter	Value
Manufacturer	Littelfuse
Series	PolySwitch®, RUSBF
Type	Polymeric
Voltage - Max	16V
Current - Hold (Ih) (Max)	1.85 A
Current - Trip (It)	3.7 A
Current - Max	40 A
Time to Trip	10 s
Resistance - Initial (Ri) (Min)	30 mOhms
Resistance - Post Trip (R1) (Max)	90 mOhms
Operating Temperature	-40°C ~ 85°C
Mounting Type	Through Hole
Package / Case	Radial, Disc
Size / Dimension	0.402" L x 0.118" W (10.20mm x 3.00mm)
Height - Seated (Max)	0.618" (15.70mm)
Lead Spacing	0.199" (5.05mm)
Approval Agency	CSA, TUV, UL
RoHS Status	ROHS3 Compliant
Product Status	Active

Substitute Part Grouping Explanation

The RUSBF185-2 has one parametric equivalent within the PolySwitch® RUSBF series: RUSBF185-AP. Substitution eligibility is determined by strict equivalence across all critical electrical and mechanical parameters:

Electrical Parameters (Must Match Exactly):

Voltage rating: 16V maximum
Hold current (Ih): 1.85A maximum
Trip current (It): 3.7A
Maximum current: 40A
Time to trip: 10 seconds
Initial resistance (Ri): 30 mOhms minimum
Post-trip resistance (R1): 90 mOhms maximum
Operating temperature range: -40°C to 85°C

Mechanical Parameters (Must Match Exactly):

Mounting type: Through hole
Package configuration: Radial, disc
Physical dimensions: 0.402" L x 0.118" W (10.20mm x 3.00mm)
Seated height: 0.618" maximum (15.70mm)
Lead spacing: 0.199" (5.05mm)

Compliance Parameters (Must Match Exactly):

Approval agencies: CSA, TUV, UL
RoHS status: ROHS3 Compliant

The RUSBF185-AP variant differs only in packaging designation (Cut Tape vs. the main part's Cut Tape specification) and inventory availability, with no electrical or mechanical parameter variations.

Parameter Comparison

Parameter	RUSBF185-2	RUSBF185-AP	Match Status
Manufacturer	Littelfuse	Littelfuse	Identical
Series	PolySwitch®, RUSBF	PolySwitch®, RUSBF	Identical
Type	Polymeric	Polymeric	Identical
Voltage - Max	16V	16V	Identical
Current - Hold (Ih) (Max)	1.85 A	1.85 A	Identical
Current - Trip (It)	3.7 A	3.7 A	Identical
Current - Max	40 A	40 A	Identical
Time to Trip	10 s	10 s	Identical
Resistance - Initial (Ri) (Min)	30 mOhms	30 mOhms	Identical
Resistance - Post Trip (R1) (Max)	90 mOhms	90 mOhms	Identical
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	Identical
Mounting Type	Through Hole	Through Hole	Identical
Package / Case	Radial, Disc	Radial, Disc	Identical
Size / Dimension	0.402" L x 0.118" W (10.20mm x 3.00mm)	0.402" L x 0.118" W (10.20mm x 3.00mm)	Identical
Height - Seated (Max)	0.618" (15.70mm)	0.618" (15.70mm)	Identical
Lead Spacing	0.199" (5.05mm)	0.199" (5.05mm)	Identical
Approval Agency	CSA, TUV, UL	CSA, TUV, UL	Identical
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Identical
Product Status	Active	Active	Identical

Engineering Selection Recommendations

Both RUSBF185-2 and RUSBF185-AP are active products manufactured by Littelfuse with identical electrical, mechanical, and compliance specifications. Selection between these parts is based on supply chain availability and packaging format requirements rather than functional differences.

The RUSBF185-2 carries 4040 units in current inventory, while the RUSBF185-AP variant maintains higher stock levels at 20400 units. Both parts hold equivalent certifications from CSA, TUV, and UL, and both comply with ROHS3 requirements. For applications requiring immediate availability or high-volume procurement, the RUSBF185-AP may offer supply chain advantages. For applications with existing design documentation specifying RUSBF185-2, direct substitution with RUSBF185-AP is electrically and mechanically valid without circuit redesign.

Frequently Asked Questions (FAQ)

Q: Can RUSBF185-AP be used as a direct replacement for RUSBF185-2?

A: Yes. Both parts are parametrically identical across all electrical characteristics (voltage, current ratings, resistance values, trip time), mechanical dimensions (physical size, lead spacing, mounting configuration), and compliance certifications (CSA, TUV, UL, ROHS3). No circuit modifications are required for substitution.

Q: What are the key electrical parameters that define this fuse family?

A: The RUSBF185 family is defined by 16V maximum voltage rating, 1.85A hold current, 3.7A trip current, 10-second trip time, 30 mOhms initial resistance, and 90 mOhms maximum post-trip resistance. These parameters remain constant across all variants in this product line.

Q: Are there any mechanical compatibility concerns when substituting between these parts?

A: No. Both RUSBF185-2 and RUSBF185-AP use identical through-hole radial disc packaging with 0.402" x 0.118" dimensions, 0.618" seated height, and 0.199" lead spacing. PCB footprints and mounting requirements are identical.

Q: What certifications apply to both parts?

A: Both RUSBF185-2 and RUSBF185-AP carry CSA, TUV, and UL approvals and comply with ROHS3 environmental standards. Certification status is identical between the two variants.

Q: Why would I choose one part number over the other if they are electrically identical?

A: Selection is driven by supply chain factors. RUSBF185-AP maintains significantly higher inventory levels (20400 units vs. 4040 units), which may reduce lead times for high-volume orders or urgent requirements. For applications with existing design documentation or procurement specifications, the original part number may be retained for traceability and documentation consistency.

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